High alumina refractory



Patented July 27 i943 Umts man ALUMINA aaraao'ronr.

Alex Edward Fitzgerald, MeriomPa., assigner to General,Rlzeir'actor'iesn Company, Philadelphia. En., a corporation ofPennsylvania appuntamenti@ 23, 1940,' serai No. 362,335 25 claims. (er.ros-.ssi

The present invention relates to high alumina refractories and theprocess of producing them.

A purpose of the invention is to produce refractories containing morethan 67%- alumina from raw minerals which are essentially hydratedalumina by methods which `4are economical and render the refractoriesfree from shrinkage at high temperature or subject to expansion at hightemperature.

A further purpose is to obtain high density with freedom from shrinkageat high temperature in refractories containing more than 67% aluminamanufactured from raw minerals which are essentially hydrated alumina. j

A further purpose is to calcine without fusing a raw numeral which isessentially hydrated alumina, to mix with Vthe calcined alumina a clayof quantity and silica content proper to cause excludes their use inordinary tonnage production.

Efforts havebeen made for many years to produce satisfactory highaluminarefractories from raw materals which are essentially hydrated alumina byordinary ceramic methods such ascalcining without fusing and ringwithout fusing, and a number of such products are available on themarket. The existing commercial products of this class have been oflimited utility because grind the raw materials to extremely fine statespansion on firing above pyrometric .cone I0, to

mold the mix into brick, to re the brick above pyrometric cone l0, andto stop firing While the brick still is capable of further expansion on`reheating to 1600 C. for ve hours.

A further purpose is to overcome excessive shrinkage in high aluminarefractory brick produced from a raw mineral which is essentiallyhydrated alumina by calcining the raw mineral by itself at atemperaturebetween pyrometric cones `lli and 30 inclusive, mixing thecalcined alumina mineral with a proper quantity of uncalcined clay ofproper silica content, forming the mix into brick and firing the brickat a temperature between pyrometric cones l to 23 inclusive, preferablyring at a temperature between pyrometric cones I0 and I6. Where the claycontains from 50 to 65% silica, from 15 to 30% of uncalcined int claywill be employed, the preferable quantity being about 20% or above andthe most desirable quantity being about 30%. Where the clay has a silicacontent of from 65% to 75%,I

from 7% to 25% of uncalcined clay will be used, preferably about 10%.Speaking generally, with uncalcined clay of -silica content from 60% to75%, from 7% to 30% of uncalcined clay will be aluminous minerals underthe extremely highA temperature of the electric furnace. These fusedlalumina refractories are substantially free from shrinkage but theirexceedingly high expense pre- Fused alumina refrac' of `subdivision andto calcine added ingredients other than the hydrated' alumina itself.

By the present invention high alumina refractories are obtained,containing at least 67% of alumina, by inexpensive and normal ceramicmethods, while at the same time excessive hightemperature shrinkage isovercome and high density is obtained. Any raw mineral may be employedwhich is essentially hydrated alumina. The commercial minerals of thistype are Drimarily diaspore, bauxite and gibbsite, varying in coposition when pure from 85% of alumina and 15% of chemically combinedWater to 65.3% of alumina and 45.7% of chemically combined Water. Thesematerials are calcined before inclusion in the high alumina brick, butthe .calcining-temperature is markedly below the fusing temperature usedin making fused alumina refractories. It is also proper to employsomewhat more impure materials for calcined alumina than l those used inmaking fused alumina. In the present invention the calcining of thehydrated alumina is accomplished in a conventionalI oil, gas or coalfired kiln at a temperature of from pyrometric cone I6 to 30 inclusive.

'- In the conventional procedure for the manu- `-brick was fired, thecommercial high alumina bricks under discussion shrink excessively,causing early failure. The shrinkage is most pronounced in thecommercial jhigh alumina bricks of high density, that is those ofspecific gravity above 2.24. 4 f

This shrinkage has hithertofore generally been attributed toinsuflicient `shrinkage of the diaspore during calcining, and variousprocedures have been devised to obtain more shrinkage and greaterdensity in calcining the diaspore. Higher calcining temperatures havebeen used and fluxes, such as phosphate rock, have been added.

However, in spite of the use of denser calcined alumina and theproduction of bricks containing such denser calcined alumina, the brickshave continued to shrink and unsatisfactory results have been obtained.

'I'he present inventor has discovered that the excessive shrinkage ofhigh alumna brick may be corrected by inclusion in the brick of theproper kind of clay in the proper amounts. No special precaution need beemployed to obtain abnormally dense or abnormally preshrunk calcinedalumina, if the proper character and quantity of clay be employed.

The generally accepted test to determine shrinkage or resistance toshrinkage of high alumina bricks is that prescribed by the AmericanSociety for Testing Materials, text C 113, schedule C. The test bricksare heated to 1600 C. (29127 F.) over a period of ve hours and held atthis temperature for ve hours. The bricks are then cooled and measuredand their percentage linear shrinkage calculated on the basis of theirlength before and after refring in this test. The curves in the figureshow percentage linear change, whether as shrinkage or expansion, as theordinate plotted against the bulk specific gravity of the brick testedas measured at the beginning of the test. The normal bulk specificgravity for high alumina. bricks produced by ceramic methods is 2.07 to2.15 grams per cubic centimeter, equivalent toa weight of 7.6 to 7.9pounds for a standard 9x41/x21/2 inch brick. Any specic gravitysubstantially exceeding 2.07

. to 2.15A is considered high and any such brick is generally referredto as a dense brick.

Curve I, whose points are represented by circles, shows the shrinkagecharacteristics of conventional high alumina brick available on themarket and manufactured by the standard companies in this field. It willbe seen that the shrinkages of these specimens are all approximately 2%or higher, and this frequently gives cause for complaint in service.

By the present invention it is possible to reduce the shrinkages to 1%or less Without resorting to unusual or expensive procedures.

Curve 2 shows the eifect on linear change of additions of variousquantities of clays of particular compositions. In curve 2 theshrinkages are-all less than 1% and are from 1.8%. to 2.9%

i less than the corresponding shrinkage values for conventional bricks.

For example, by mixing. the calcined alumina obtained from raw` hydratedalumina mineral With`a. clay of approximately 50% silica and.45% aluminain the proportions of 90% calcined alumina and 10% clay, a productshrinking 2.2% was obtained as shown by the point A on curve I; Wherethe proportions were changed to 80% of calcined alumina to of flintclay. the

` shrinkage was reduced to 0.6% as shown by the point B and where theproportions were ,changed to 70% of calcined alumina and 30% of intclay, shrinkage was entirely eliminated and the brick expanded 0.4% asshown by the point C on curve 2. With each 10% increase in flint clayand corresponding reduction in calcined hydrated alumina mineral, theshrinkage was reduced by an average of 1.3% in spite of reduction indensity of the brick. Based on equal density (see table below), thisreduction in shrinkage was actually 1.8% for each 10% increase in thisclay. 'I'he effect of the quantity of the clay will be evident fromthese experiments.

The same eiect which was obtained in these experiments by adding arelatively large quantity of iiint clay having a silica content of aboutmay be obtained by adding' a smallerquan-l LINEAR CHANGE (A. S. T. M.CH3-Schedule C) [Based on equivalent bulk specific gravities]Raw,hydrous alumina mineral in calcined v form .percent.. A90 80 70 Claycontaining 50% silica do.- l0 20 3o Clay containing 73% silica .doLinear change 12.2 10.4 21.4 21.2

l Shrinkage.

2 Expansion. 1 This table, based on bricks of equal bulk speciegravities, best shows the effects of change in quantity of a claycontaining 50% silica or employing a clay containing 73% of silica.

In brick produced according to the present invention, the lineardimension of the Arefractory after reheating at 1600 C. for five hoursis from 99 to 102% of the initial dimension. Thus Where the naldimension is 99% of the initial dimension, there is 1% shrinkage andwhere the final dimension is 102% of the initial dimension, there is 2%expansion.

It is important that the great bulk of the clay be used in Yraw oruncalcined form, although, of course, it will be understood that theclay may be preliminarily dried to remove moisture, say at a temperaturebelow 300 C. (572 F.). If the bulk of the clay included i-n the brickwere in the form of calcined clay or grog, the chemical reaction withthe calcined alumina mineral which causes expansion during reheating orcounteracts shrinkage during reheating could not take placeLthe abilityto cause expansion being a characteristic of the raw clay. It is furtherundesirable to include calcined clay in the refractory mix becausecalcining destroys whatever bonding property the claymay possess.I

In the prior art it has been proposed to mix the alumina mineralwithclay prior to calcining and calcine the alumina mineral and claytogether. This is highly undesirable and to be avoided in the procedureaccording to the present invention, since if the alumina mineral andclay be calcined together, a chemical reaction will take place duringthe calcining causing ex- ,quantity of clay required is interrelated tothe silica content of the clay, although not in afslmple relation.

Of flint clays containing from 50 to 65 silica it is desirable to empmyfrom 15 to 30%, the

quantity preferably being about 20% and most desirably about 30%. Acontent of approximately 30% of-int clay` containing from 50 to 65%silica will insure an expanding brick.

Of uncalcined iire clayV containing Afrom 65 to '75% of silica, from 7to 25% will desirably be employed, from to 20% being the more desirablerange and for best results the clay. contentbeing about 10%; Very goodresults .have .been obtained using Woodbury (Pennsylvania) r'e clay, aclay containing from 65 to 75% of silica. The siliceous type ofcl'ayknown as Woodbury occurs also in New Jersey,

With uncalcined iire clay containing from 60 to '15%` of silica, thequantity used will range from 7 to 30%, the higher quantities normallybeing employed with the clay of lower silica content within this range.I I have discovered that only 10% to` 15% of a raw re clay containing 65to '75% of silica need be used to substantially eliminate shrinkage in ahigh alumina brick of the type under discussion. This is highly usefulsince with calcined alumina of the same alumina content andsamedensityit is possible to produce brick pf higher alumina content and higherdensity'than'where larger quantities of uncalcined flint clay oflowersilica content are employed. v

If we assume that a brick of 72% alumina content is required, this canbe made in one of two ways in accordance vvith the present invention.Seventy per cent of raw hydrous alumina mineral in calcined form may beused with 30% of uncalcined flint clay containing about 50% silica,

bring about more shrinkage at a .given temperaor 90% of raw hydrousalumina mineral in calcined form may be used with 10% of uncalcined reclay containing say 73% of silica. Interv 3 mediate amounts of rawhydrous alumina mineral in calcined form may be used with intermediate iquantities of clay where the silica content of the clay lies between 50and 75%. With a iire clay containing more than 73% of silica, more than90% of'raw hydrous alumina mineral in calcined form may be used. Ifthemix contains 70% of -raw hydrous alumina mineral in calcined formwith of a clay containing of silica as above described, the aluminacontent of the calcine should be approximately 83%. If the mix contains90% of raw hydrous alumina mineral in calcined form and 10% of a claycontaining 73% of silica (24% of alumina), the aluminacontent of thecalcine need be only '77%. Thus it will be seen that the alumina contentof the available diaspore, baux* ue or gibbsite determines the questionas to whet ier one clay should be used rather than another in thepresent invention. e A

The preparation of the ,calcine from the raw hydrous alumina mineralwill vary according to the character of the raw material, the additions.of fluxes made to facilitate shrinkageA during calcining and/or thedensity requiredin the cal` cine. If raw hydrous alumina mineral isavailable in lump form and no fluxes need be added, the lumps may beplaced conveniently in intermittent orcontinuous kilns and calcined. Ifthe raw hydrous alumina mineral is not available in lump form or iffluxes are to be added, the raw hydrous alumina mineral may be crushed,ground, molded into lumps (dobies) and sei before calcining Ifpreferred, iinely divided materials may be calcined, as for example in arotary kiln. Any well-known flux such as magnesite or phosphate rock maybe employed to facilitate shrinkage'. If the materials are very finelyground, as for example to 65 or 100 mesh per linear inch and made intodobies, shrinkage is further facilitated.

f condition 95% of the particles mesh. 0n the other' hand,- the calcinedalumina..V4

`cedures for sizing are available.

ture of calcining, or a given shrinkage at a lower temperature ofcalcining.

Where materials of 'diierent alumina content,

must be blended to obtain the desired alumina percentage, this may bedone after calcining or if the materials are nely ground,beforelcalcining.

The density which mustbe obtained from calcining the raw hydrous aluminaminerals depends upon the amount of clay to be added andthe densityrequired in the nished brick. For a given density in the nished brickthe density of the calcined material must be increased as the amount ofclay is increased. For any given mix the density of the calcinedmaterial must be in` creased if the density of the finished brick is tobe increased. For instance, to produce a brick having a density of 2.24grams per cubic centimeter from a mix containing 70% of raw hydrousalumina mineral in calcinedform and 30% of uncalcined re clay, the bulkspecific gravity of they calcined alumina must be 2.58. If, on the otherhand, the mix contains 90% of raw hydrousl sity `oi" the calcine isobtained by higher'iiring temperature, ner grinding prior to calcining,

compact moldingof the dobiesand addition of fluxes. j f s There is adefinite advantage in obtaining bulk specific gravities of the finishedbrick in excess of 2.24, and such brick canl readily be produced inaccordance with theinvention. In fact, bulk specic gravities as high as2.42 'or higher-may be obtained by the procedure of the invention.

I nd that the calciningtemperature may range between pyrometric cones I6and 30 inclusive. It is desirable that the particles of the mix beground and graded las to size. Various pro- The entire batch may beground and screened to a particle size of 6 to 8 mesh per linear incunder which pass 6 'to 8 may be 6 or 8 mesh rper linear inch and theclay -mesh per linear inch. On the other hand, part o'f the calcinedalumina and part of the clay may be ground'to 35 mesh'or finer, theremaining portion'of the mix being of the orderl of 6 or'8 `mesh. For,best results certain intermediate sizes of" particles should be entirelyor almost entirely eliminated to secure gap sizing. A typical screenanalysis of the entire mix would be as follows:

, Per cent- Retained on 28mesh 45 to'50 Retained on 48 mesh 10 to 0 YPassing through 48 mesh 45 to 50 'rota1 ",100

` If the particles passing 28 mesh and retainedv on 48 mesh are reducedto a minimum in normal grinding and screening, the amount of coarseparticles retained on 28 mesh and fine particles passing 48 mesh may bevaried to' suit the re- `quirements. Preferably no particles larger than3 mesh -Will be employed. The coarse particles retained on 28 mesh mayvary from 30 to 70% and the fine particles passing through 48 mesh mayvary from 70 to 30%. It is preferred to include all the clay in the fineparticles. By gap sizing the product is made more uniform and better inappearance. I

There are various alternative procedures which may be used in preparingand molding the mix. The particles of calcined alumina and clay,suitably sized, can be intermixed and moistened with water duringgrinding and screening, or in `a conventional pug mill or pan mixerafter grinding and screening. The best kown pan type mixers are theSimpson, Lancaster and Clearfield, but many other types are available.

During the mixing some temporary bond such as glutrin, goulac, dextrinor the like may be added to provide high strength and hardness aftermolding and drying. The molding may be accomplished by hand moldingmethods, with air hammers or with presses of any suitable type. Forbes't results the molding pressures should exceed 1500 pounds persquare'inch.

Following molding the refractory may optionally be dried before firing.

Firing may be accomplished in intermittent or continuous kilns usingfiring temperatures ranging between pyrometric cones I and 23 inclusive.

In normal operation the ring temperature will v range from pyrometriccone I0 to I6 inclusive. The expansion eect of the raw fire clay iseffective during ring at lowtemperature (as low as pyrometric cone I0),and continues aslong as excessive firing temperatures are not used. 'Ifthe firing temperature is carried above pyrometric cone 23, theexpansion effect of the re clay is destroyed, and the brick will exhibitexcessive shrinkage when reheated to 1600 C'. for ve hours. If thefiring be stopped at pyrometric cone 23 or below, the fired brick willbe of low reheat shrinkage or will expand if reheated to 1600 C. forfive hours. There is no advantage and possibly a slight disadvantage infiring above pyrometric cone IS but there is a .very definitedisadvantage in firing above pyrometric cone 23.

It is desired to retain, after firing, the capability of expandingduring reheating of the brick.

An important advantage of the product of the present invention is thatit develops high strength and hardness with elimination of seriousshrinkage by ring at these very moderate temperatures, rather thanrequiring the high firing temperatures of some of the prior artprocesses. High firing temperatures are not only expensive to maintain,but they increase the losses in ring and reduce the accuracy of sizingof the fired shapes.

In many prior art ring procedures for highl alumina brick it has beennecessary. to employ box setting, that is, supporting of unfired brickson previously fired bricks to avoid warping, twisting and otherdeformation during firing. In the present invention box setting is notnecessary and economy results by avoiding it. The negligible shrinkageof the bricks in the present process makes it possible to meet severesize specications with ease.

While the fundamental mix of the present invention employs raw hydrousalumina minerals in calcined form, a small amount, up to of the mix, maybe in raw form. Likewise, while the fundamental mix of the inventionemploys uncalcined or raw fire clay, a small amount, up

to one-fourth of the quantity of ire clay used. 75

4in are percentages by Weight on a calcined basis notwithstanding thatthe particular materials referred to may be used in a raw or uncalcinedform. All mesh sizes stated herein are Tyler standard mesh per linearinch.

In view of my invention and disclosure varations and modifications tomeet individual whim or particular need will doubtless become evident toothers skilled in the art, to obtain all or part of the benefits of `myinvention without copying the structure shown, and I, therefore, claimall such in so far as they fall within the reasonable spirit and scopeof my invention.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

1. The process of producing high alumina refractory, which comprisescalcining a raw mineral which is essentially hydrated alumina by itselfwithout fusion, mixing the calcined alumina mineral with from 7 to 30%of uncalcined clay containing from 60 to 75% silica, molding the mix,firing the mix at a temperature above pyrometric cone I0 and stoppingthe ring while the refractory is still capable of further expansion onreheating;

2. 'I'he process of producing high alumina refractory, which comprisescalcining a raw mineral which is essentially hydrated alumina by itselfWithout fusion, mixing the calcined alumina mineral with from 15 to 30%of uncalcined flint clay containing from to 65% silica, molding the mix,firing the mix at a temperature above pyrometric cone l0 and stoppingthe ring while the refractory is still capable of further expansion onreheating.

3. The process of producing high alumina refractory, which comprisescalcining a raw mineral which is essentially hydrated alumina by itselfwithout fusion, mixing the calcined alumina mineral with from 7 to 25%of uncalcined clay containing from 65 to 75% silica, molding the mix,firing the mix at a temperature above pyrometric cone I0 and stoppingthe firing while the refractory is still capable of further expansion onreheating.

4. The process of producing a refractory containing more than 67%alumina having a linear dimension after reheating to 1600 C. for vehours of from 99 to 102% of the initial dimension, from a raw mineralwhich is essentially hydrated alumina, which comprises calcining the rawmineral which is essentially hydrated alumina by itself at a temperaturebetween Ipyrometric cones 16 and 30' inclusive, mixing the calcinedalumina mineral with'from 7 to 30% of uncalcined clay containing from to75% silica, forming the mix into brick and ring the brick at atemperaturebetween pyrometric cones I0 and 23 inclusive. a f

5. The process of producing a diaspore refractory containing more than67% alumina and having a linear dimension after reheating to 1600 C. forve hours of from 99 to 102% of the initial dimension, which comprisescalcining diaspore by itself at a temperature between pyrometric conesI6 and 30 inclusive, mixing the calcined diaspore with from 7 to 30% ofuncalcined clay containing from 60 to 75% silica, forming the mix intobrick and firing the brick at a temperature between pyrometric cones l0and 23 inclusive.

6. The process of producing a bauxite refractory containing more than67% alumina and having a linear dimension after reheating to 1600 C. foriive hours of from 99 to 102% of the initial dimension, which comprisescalcining bauxite by itself at a temperature between pyrometric cones i6and 30 inclusive, mixing the calcined bauxite with from 'I to 30% ofuncalcined clay containing from 60 to 75% silica, forming the mixintobrick and ring the brick at a temperature between pyrometric cones I and23 inclusive.

7. The process of producing a gibbsite refractory containing more than67% alumina and having a linear dimension after reheating to 1600 C. foriive hours of from 99.to 102% of the initial dimension, which comprisescalcining gibbsite by itself at a temperature between pyrometric conesI6 and 30 inclusive, mixing the calcined gibbsite with from 7 to 30% ofuncalcined clay containing from 60 to 75% silica,

forming the mix into brick and iring the brickat a temperature betweenpyrometric cones l0 and 23 inclusive.

8. The process-of producing a refractory containing more than 67%alumina having a linear dimension after reheating to 1600 C. for fivehours of from 99 to 102% of the initial dimension and of high densityfrom a raw mineral which is essentially yhydrated alumina, whichcomprises calcining the raw mineral which is essentially hydratedalumina by itself at a temperature between pyrometric cones I6 and 30inclusive, mixing the calcined alumina mineral with from to 30% ofuncalcined iiint clay containing from 50 to 65% silica, forming the mixinto brick and firing the brick at a temperature between pyrometriccones I0 and 23 inclusive.

9. The process of producinga refractory containing more than 67% aluminahaving a linear dimension after 'reheating to1600? C. for ve` cones` I6and 30 inclusive, mixing the calcined diaspore with from l5 to 30% ofuncalcined iiint clay containing from to 65% silica, forming the mixinto brick and iiring the brick at a temperature between pyrometriccones I0 and i6 inclusive.

l2. The process of producing a bauxite refractory containing more than67% alumina having a linear dimension after reheating to 1600 C. for vehours of from 99 to 102% of the initial dimension and having a bulkspecic gravity in excess of 2.24, which comprises calcining bauxite byitself at a temperature between pyrometric cones I6 and 30 inclusive,mixing the calcined bauxite with from 15 to 30% of uncalcined flint claycontaining from 50 to 65% silica, forming themix into brick and'iiringthe brick at a temperature between pyrometric cones I0 and I6 inclusive.

13. The process of producing a gibbsite refractory containing more than67% alumina having a linear dimension after reheating to 1600 C. for vehours of from 99 to 102% of the initial dimensionv and having a bulkspecii'lc gravity in excess of 2.24, which comprises calcining gibbsiteby itself at a temperature between pyrometric cones I6 and 30 inclusive,mixing the calcined gibbsite with from 15 to 30% of uncalcin'ed int claycontaining from 50 to?65% silica, forming the mix into brick yandiringthe brick at a temperature between pyrometric cones I0 and I6 inclusive.

14. `The process of producing a refractory containing more than 67%'alumina having a linear dimensionafter reheating to 1600 C. for vehours of from 99 to 102% of the initial dimensionfand of high densityfrom a raw mineral which is essentially hydrated alumina, whichcomprises calcining the raw mineral which is essentially hydratedalumina by itself at a temperature between pyrometric cones I6 and 30inclusive, mixing the calcined alumina mineral with from 7 to 25% ofuncalcined clay containing from to 75% silica, forming the mix intobrick and firing the brick at a temperature between pyrometric cones I0and 23 inclusive.

forming the mix into brick-and firing the-brick at a temperature betweenpyrometricv cones I0 and 23 inclusive.,

liu. The process of producing a refractory containing more than 67%alumina whi h permanently expands on reheating to 1600 C. for vehoursand has a bulk specific gravity in excess of 2.24" from a raw mineralwhich is essentially hydrated alumina, which comprises calcining the rawmineral which is essentially^hydrated alumina. by itself at atemperature between pyrometric cones I6 and 30 inclusive, mixing thecalcined aluminamineral with about 30% of uncalcined int clay containingfrom 50 to 65% silica,`

forming the mix into brick and ring the brick at a temperature betweenpyrometric-cones I0 and 23 inclusive.

ll. The process of producing a diaspore refractory containing more than67% alumina having a linear dimensionl after reheating to 1600 C. for vehours of from 99 to102% of the initial dimension and-having a bulkspecic gravity in excess of 2.24, which comprises calcining diaspore byitself at a temperature between pyrometric 15; T'he process of producinga refractory containing'more than 67% alumina having' a lineardimension, after reheating to 1600 C. for iivel hours of from 99 to 102%of theinitial dimen-v sion and of high density from a raw mineral whichis essentially hydrated alumina, which comprises calcining the rawmineral which is `es sentially Vhydrated alumina `by itself at atemperature between pyrometric cones I6 and 30 inclusive, mixing thecalcined alumina mineral with about 10% of uncalcined clay containingfrom v65 to 75% silica, forming the mix into brick i and ring the brickat a temperature between pyrometric cones I0 and 23 inclusive.

'16. The process of producing a refractory containing more than 67%alumina havinga lineary dimension after reheating to 1600 C". for vehours of from 99 to 102% of the initial dimension :and of high densityfrom a raw mineral which is essentially hydrated alumina, whichcomprises calcining the raw mineral which is essentially hydratedlalumina by itself at a temperature between pyrometric cones I6 and 30inclusive, mixing the calcined alumina'mineral with about10% Woodburyclay, forming the mix into brick and ring the brick at a temperaturebetween pyrometric cones I0 and 23 inclusive.

17, The process of producing a diaspore refractorycontaining more than67% alumina havtory containing more than 67% alumina having a lineardimension after reheating to 1600 C. for five hours of from 99 to 102%of the initial dimension and having a bulk specic gravity in excess of.2.24, which comprises calcining the bauxite by itself at a temperaturebetween pyrometric cones I6 and 30 inclusive, mixing the calcinedbauxite with from 7 to 25% of uncalcined clay containing from 65 to 75%silica, forming the mix into brick and ring the brick at a temperaturebetween pyrometric cones I0 and I6 inclusive.

19. The process of producing a refractory containing more than 67%alumina having a linear dimension after reheating to 1600"y C. for vehours of from 99 to 102% of the initial dimension and having a highdensity, from a raw mineral which is essentially hydrated alumina, whichcomprises calcining the raw mineral which is essentially hydratedalumina by itself at a temperature between pyrometric cones I6 and 3l)inclusive, forming from the calcined alumina and uncalcined flint claycontaining from 50 to 65% silica, a mix containing from to 30% of un-vhours of'from 99 to 102% of the initial dimension and having a highdensity, from a, raw mineral which is essentially hydrated alumina,which comprises calcining the raw mineral which' is'.

essentially hydrated alumina by itself at a temperature betweenpyrometric cones I6 and 30 inclusive, forming from the calcined aluminaand uncalcined iiint clay containing from to 75% silica, a mixcontaining from 7 to 25% of uncalcined flint clay having from 30 to 70%oi particles between 3 and 28 mesh per linear inch and from to 30% ofparticles below 48 mesli per linear inch, molding the mix into brick andring the brick at a temperature between pyrometric cones l0 and 23inclusive.

21. A red refractory brick containing morey than 67% alumina having abulk specic gravity in excess of 2.24 and comprising a raw mineral whichis essentially hydrated alumina in calcined unfused form and from 15 to30% of previously uncalcined int clay containing from 50 to 65% -ofsilica, the brick having a linear dimension after reheating to 1600 C.for five hours of from 99 to 102% of the initial dimension.

22. A red refractory brick containing more than 67% alumina having abulk specic gravity in excess of 2.24 and comprising a raw mineral whichis essentially hydrated alumina in calcined unfused form and from 7 to25% of previously cie gravity in excess of 2.24 and comprising diasporein calcined unfused form and from 7 to 30% of uncalcined clayvcontaining from 60 to silica, thebrick permanently expanding onreheating'at 1600 C. for ve hours.

24. As an intermediate product of manufacture, a refractory brickcontaining in excess of 67% alumina which consists of raw hydratedalumina mineral in calcined unfused form and from 15 to 30% ofuncalcined int clay containing from 50 to 65% of silica.

25. As an intermediate product of manufacture, a refractory brickcontaining in excess of 67% alumina which consists of raw hydratedalumina mineral in calcined unfused form and from 7 to 25% of uncalcinedclay containing from 65 to 75% silica.

ALEX EDWARD FITZGERALD.

